Temperature measurements are widespread and essential in many fields of modern life, such as industry, science, medical care and many other basic human needs. A lot of processes in industry are temperature controlled or strongly affected by temperature. Therefore, accurate temperature measurements are required for carrying them out properly. The same requirements apply also in science, when experimentation and research often require temperature sensing. Human body temperature measurements are mandatory in many cases. Accurate measurement of human body temperature is carried out as a routine in hospitals and clinics and is generally required for medical care in view of its symptomatic significance.
Mercury thermometers are used frequently for measuring the temperature of the human body orally, in the axilla or rectally. However, in spite of the fact that such measurements are in themselves accurate, they often poorly reflect the inner temperature of the human body, since there is a substantial difference between said temperature and that of the sensed area and, further, the temperature that is read depends of the way the thermometer tip is held in the measurement. Another reason for inaccuracy is associated with different modes of operation of the thermometer. For instance, if the patient is a child, using the thermometer orally, the heat conduction from his mouth to the thermometer may vary according to the orientation of the tip in the child's mouth and the fact that he opens it from time to time. Another disadvantage of the mercury thermometer is its fragility. In addition, it should be sterilized after each use.
Oral and rectal measurements are also inconvenient for the patient, and in some cases may even be painful. Surface or external measurements, such as by thermometers attached to the skin, are less inconvenient but even less accurate. Optimally, these thermometers measure the skin temperature, which may substantially differ from the relevant inner body temperature by as much as 10.degree. C. and even more, if the contact with the skin is poor. Thermal conduction and heat flow affect surface temperature measurements. For example, the human body is not well insulated from the ambient and there is a constant heat flow from the skin to the ambient and from the body core to the skin. Thus, under normal conditions, the skin temperature is always colder than the core temperature to be measured. In addition, thermal conduction between the skin and the thermometer is affected by several factors, such as adhesion and skin humidity. Additionally, heat is lost by the thermometer to the ambient in an amount depending on the insulation of the thermometer.
Another disadvantage associated with conventional thermometers is the time required to take a temperature. At least a minimum time, which may be more than three minutes, is needed for a reasonable measurement accuracy. Some patients, for instance children, do not stand such relatively lengthy measurements. Further, in hospitals, reading the temperature of each patient several times a day requires an unacceptable part of the nurse's duty time.
Other thermometers use an Infra-Red technology, thereby reducing the measurement time. Temperature is read by inserting the sensor into the ear channel measuring the amount of the IR radiation emitted from the channel, and converting it to temperature values. Still, this measurement is relatively expensive, and often does not correlate well with the body temperature.
U.S. Pat. No. 3,702,076 discloses an electronic thermometer, which provides a temperature measurement output as a direct digital, display. U.S. Pat. No. 3,942,123 describes an electronic thermometer based on an electrical bridge with a thermistor in one arm of the bridge. A shunting impedance is switched into and out of the balancing arm of the bridge in a manner providing indication about the measured temperature, according to the thermistor resistance value. U.S. Pat. No. 3,926,053 describes an apparatus of non-contact surface temperature determination on a rotating part, which comprises a sensing probe unit for temperature and distance detection and a capacitive excursion measurement system. However, each apparatus described in said patents provides only indications about the surface temperature, and still lacks the core temperature measurement capability.
It is an object of the present invention to provide a method and an apparatus for accurate measurements of body core temperatures, which overcome the drawbacks of prior art methods and devices.
It is another object of the invention to provide a non-invasive method and apparatus, which permit the accurate estimation of body core temperature from temperature measurements external to the body.
It is a further object of the invention to provide a method and apparatus for the estimation of body core temperatures, which permit to reduce the time required for the measurement without significant loss of accuracy.
It is a still further object of the invention to provide a method and apparatus which achieve the aforesaid objects in the measurement of the human body temperature without causing discomfort to the patient.
Other purposes and advantages of the invention will appear as the description proceeds.